Democrat John Edwards has left the race for the White House - without backing any of his rivals - after failing to win a single party nomination contest.
Mr Edwards, 54, announced the end to his second White House bid on a visit to New Orleans.
He had lost Iowa's caucuses, came third in New Hampshire, admitted getting his "butt kicked" in Nevada, and came third again in his native South Carolina.
In the Republican field, Rudy Giuliani is also expected to drop out later.
The ex-New York Mayor, who came a distant third in Florida's primary on Tuesday, is expected to back John McCain, said two of his allies, New York congressman Peter King and Senate Majority Leader Joe Bruno.
The remaining Republican candidates will go head-to-head in a televised debate on Wednesday in Simi Valley, California.
Their two front-runners are Arizona Senator McCain, who won in Florida, and ex-Massachusetts Governor Mitt Romney.
Born 1953 in Seneca, South Carolina; millworker's son
Personal-injury lawyer 1977-1998
US senator for North Carolina 1999-2005
First ran for White House 2004 - wanted to reform healthcare and scrap Bush tax cuts for rich
Lost nomination to John Kerry; became his running mate
Married to Elizabeth Edwards with three surviving children
Mr Edwards told supporters in New Orleans, where he launched his latest White House bid in 2006: "It's time for me to step aside so that history can blaze its path.
"We do not know who will take the final steps to 1600 Pennsylvania Avenue. But what we do know is that our Democratic Party will make history."
He did not endorse either of the two current Democratic front-runners: New York Senator and former First Lady Hillary Clinton or Illinois Senator Barack Obama.
But he said he had spoken to both of them by telephone and had received their assurances that they would place the fight against poverty at the centre of their campaigns.
Mr Edwards's wife Elizabeth, 58, announced last year her breast cancer had returned, but an Edwards aide told CNN television his reasons for dropping out had nothing to do with her health.
The impact of Mr Edwards's decision is expected to become clear on Super Tuesday next week, when some two dozen states hold nominating contests.
A recent poll by Associated Press-Yahoo said 40% of Edwards supporters said their second choice was Mrs Clinton, while a quarter chose Mr Obama.
Mr Obama, campaigning in Denver, Colorado, said Mr Edwards had spent a "lifetime fighting to give voice to the voiceless".
In Arkansas, Mrs Clinton said in a statement: "John ran with compassion and conviction."
Mr Edwards fought for his party's nomination in 2004, losing out to John Kerry, but ran a strong enough second in the race to stand as vice-president.